This invention relates to a method of and apparatus for honing a recess of circular cross-section in a workpiece. The apparatus has a honing tool which is reciprocable on a vertical guide of the machine frame and which is simultaneously rotatable, the tool being releasably attached to one end of a hollow honing rod secured to a cross-member and having grinding members which are displaceable radially of the longitudinal axis of the recess in the workpiece via adjusting means extending longitudinally through the honing rod.
In one prior art construction of a honing apparatus of the kind specified the cross-member is vertically reciprocated by thrust piston units, two vertical supports of the machine frame acting as at least an indirect guide for the cross-member. The rotary movement of the honing rod is derived from worms extending vertically and laterally through the cross-member and driven by chain drives disposed in the cross-member. The worms are rotated by electric motors, through chain drives. The grinding members of the grinding tool are displaced radially of the longitudinal axis of the recess in the workpiece to be machined by adjusting means extending through the hollow honing rod. The central adjusting means is operable by a hydraulic thrust piston unit which rotates with the honing rod. However, this arrangement necessitates hydraulic connections which give rise to leaks. The hydraulic thrust piston unit can also be directly attached to the cross-member, in which case the piston rod is carried on an axial bearing. However, both of these known embodiments prevent the drive motor from being connected directly to the honing rod, i.e., without an intermediate transmission in the form of chain drives.
In addition to these disadvantages, the prior art construction has another considerable defect, namely that the vertical reciprocation of the honing tool is fairly noisy and very uneven. The reason for this is not only the relatively considerable expense of open and closed loop control devices for reversing the cross-member from the upward to the downward movement and vice versa and the resulting sources of vibration, but also the inertia of the reversing elements. The result is that considerable shocks occur on reversal of the cross-member which, as well as heavily stressing the static and dynamic structural elements and making an unpleasant noise, also have detrimental effects on the quality of the workpiece surface being machined. Furthermore, the force exerted to move the cross-member must take into account the weight of the cross-member plus the weight of the honing rod and honing tool in addition to the force which is required for the abrasion of the workpiece surface. In the case of downward movement, for instance this means that the cross-member must as a rule be braked, while during the upward movement the force exerted must ensure the required abrasion of the workpiece surface and the lifting of the cross-member, the honing rod and the honing tool.
Another disadvantage of the known apparatus is the insufficient resiliance of the electric drive motors and the transmission devices connected thereto, which in spite of safety devices frequently cause the honing rod to break or result in the destruction of the honing tool, more particularly if a honing tool suddently gets jammed due to the masses which even when stopped continue to rotate to a limited extent. The honing tool is very liable to get jammed more particularly in blind recesses such as blind bores.